The present invention is generally related to equipment and systems for the production of oil and gas, and more particularly to a surface safety valve hydraulic actuator for offshore use and having separately removable, installable and interchangeable wirecutting and non-wirecutting spring modules for use with the same hydraulic cylinder and bonnet.
In order to reduce the risks inherent in locating, accessing, and producing oil and gas, the equipment and systems used in the endeavor are typically provided with safety devices for preventing, interrupting, or stopping the flow of oil or gas in the event of an emergency. Such devices include surface safety valves, which are intended to be closed rapidly to shut off the flow of oil or gas when an emergency occurs, or when it is otherwise desired to close the valve quickly. Such safety valves are typically provided with hydraulic actuators designed to keep the valves open through application of pressurized hydraulic fluid to a piston in the actuator, and to close the valve through application of spring force when the pressurized hydraulic fluid is lost through hydraulic control system failure or is otherwise no longer applied to the piston. Such an actuator may be termed fail-safe-closed, since in the event of an emergency causing loss of hydraulic control fluid pressure, the actuator will automatically cause the valve to assume the "safe" or closed state.
From time to time, such surface safety valves must be operated during periods when wirelines, such as logging cables or the like, are employed for running various tools and equipment through the valves into the well. During such periods, for example during workover operations or when the well is performing poorly, the surface safety valve hydraulic actuator must be able to close the valve completely and rapidly upon shutoff or loss of hydraulic control fluid pressure and, in addition, it must be able to shear any wireline up to, for example, 7/32" braided line, which happens to be extending through the valve at the time. The actuator must have this wirecutting capability because there may not be enough time during an emergency and prior to closing of the safety valve to remove the wireline and its associated tools from the well.
During normal production operations, the hydraulic actuators for the surface safety valves do not require this wirecutting capability. Since the periods during which wirecutting capability is required are typically more infrequent and of shorter duration than the periods of normal production operations, more often than not the additional wirecutting capability of the hydraulic actuators is superfluous. In the past, however, if wirecutting capability was ever to be needed at a particular location, the operator had the choice of either installing a wirecutting actuator permanently, or of temporarily installing a complete wirecutting actuator assembly in place of a non-wirecutting actuator assembly only when the wirecutting capability was needed. The first of these two alternatives is uneconomical, since a wirecutting actuator is of necessity larger and more expensive than a non-wirecutting actuator, and the operator is paying more for the wirecutting capability when most of the time he does not require it. The second of these two alternatives is also uneconomical, since it typically involves inordinately time-consuming actuator assembly removal and installation procedures, equipment handling difficulties due to the weight of the actuator assemblies and the limited space on offshore facilities in which to work, and excess inventory of actuator assemblies.